The expression patterns of 20-25 previously identified candidate genes, implicated in plant hormone biosynthesis, transport and response will be analyzed by qRT-PCR method. Association of expression with the specific traits of apple fruit ripening pattern and quality attributes will be assessed.

3.Progress Report

This project relates to objective 1 of the associated in-house project which seeks to identify factors that influence postharvest fruit quality and development of market limiting physiological disorders. Plant hormones are the major regulators on apple fruit ripening process and quality. Understanding the molecular mechanism of plant hormone regulation on cultivar-specific fruit quality and ripening patterns would be the first step in developing molecular breeding tools, such as gene-specific functional markers. These tools are important for improving precision and efficiency in apple breeding, and could also potentially generate innovative technology to manage ripening and quality. Several candidate genes based on our previous global gene expression analysis were selected for further study regarding their specific association with apple fruit ripening behavior. Phenotypes such as fruit ripening date, firmness and size for selections in a cross population were characterized and categorized. Fruit from 12 individuals in each phenotypic group (early or late-ripening; firm or soft fruit; small or large fruit) were selected for gene expression analysis. Gene-trait association analysis (associated segregation) suggests that the expression levels of a few candidate genes with the annotated functions in plant hormone metabolism, transport and response show significant correlation with these phenotypes. For more systematic analyses of these candidate genes for their specific association with ripening season and fruit texture traits, six elite cultivars with distinct ripening behavior (ripening dynamics and ripening time) are currently being characterized. Selected candidate genes are being aligned with the currently available apple genome sequence for more accurate interpretation of their roles in regulating fruit ripening and quality. Progress is monitored through annual submission of written reports to the funding organization.